TKD defines this as food. KGT expands the meaning to beverages as well.

When asked to distinguish between [the nouns quv and batlh], Maltz said, "tlhIngan Soj 'oH — not bIyaj," literally, "It is Klingon food — you will not understand," using Soj food in its idiomatic sense of matter, concern, affair.

This idiomatic meaning of the verb Soj can also be used to express the idea of "mind your own business." In these sentences, it means "concern", that is, something of interest or importance to someone.